While no war was declared between Poland and the Soviet Union, the relations were tense, and eventually broke down in 1943 in the aftermath of the revelations of the Katyn massacre.

"[1][9] After the fall of communism, the new Polish government supported the investigation, carried out by the Institute of National Remembrance (IPN), which classified it as a communist crime.

[1] In 1995 the Russian government confirmed that 590 Polish citizens were arrested and 579 were put on trial, but that there is no information on their subsequent fate.

[1] A symbolic monument has been built in the village of Giby, where a mass grave was found (these were later proven to belong to German soldiers from a nearby field hospital).

[2][8] In May 2011, Russian historian Nikita Petrov declared that he found a KGB document proving that the Poles were executed by NKVD.

[2] This has evoked interest in Polish mainstream press and from the IPN, which declared that it would seek the documents located by Pietrov for further analysis.